Seat mechanism



FIG. 1 is a front perspective view of a seat mechanism according to my design;

FIG. 2 is a top view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a rear view thereof;

FIG. 6 is a left side view thereof; and,

FIG. 7 is a bottom view thereof.

Where included, broken lines showing environment or structure are for illustrative purposes and form no part of the claimed design. 

The ornamental design for a seat mechanism, as shown and described. 